Method for preparing p-hydroxymandelic compounds in stirred reactors

Abstract

The process allows the preparation of a p-hydroxymandelic compound, comprising at least one step of condensation of at least one aromatic compound bearing at least one hydroxyl group and whose para position is free, with glyoxylic acid, the condensation reaction being performed in at least one reactor equipped with at least one mixing means, the specific mixing power being between 0.1 kW/m 3 and 15 kW/m 3 . In addition, the invention also relates to a process for preparing a 4-hydroxyaromatic aldehyde by oxidation of this p-hydroxymandelic compound.

1 . A process for preparing an aromatic compound bearing at least one —CHOH—COOH group para to a hydroxyl group, comprising condensing, in a condensation reaction performed in at least one reactor equipped with at least one mixer having a specific mixing power of between 0.1 kW/m 3  and 15 kW/m 3 , at least one aromatic compound bearing at least one hydroxyl group and whose position para to the hydroxyl group is free, with glyoxylic acid. 
     
     
         2 . The process as claimed in  claim 1 , characterized in that the at least one aromatic compound is selected from the group consisting of phenol, o-cresol, m-cresol, 3-ethylphenol, 2-tert-butylphenol, guaiacol and guetol. 
     
     
         3 . The process as claimed in  claim 1 , wherein the condensation reaction is performed in a batch regime or in semi-continuous regime. 
     
     
         4 . The process as claimed in  claim 3 , wherein several reactors are run in parallel. 
     
     
         5 . The process as claimed in  claim 1 , wherein the condensation reaction is performed in a reactor in continuous regime. 
     
     
         6 . The process as claimed in  claim 5 ,  claim 1 , wherein the condensation reaction is performed in a cascade of several reactors. 
     
     
         7 . The process as claimed in  claim 6 , wherein the last reactor of the cascade of reactors is a finishing reactor. 
     
     
         8 . The process as claimed in  claim 1 , wherein the specific mixing power of the mixer is between 0.1 kW/m 3  and 12 kW/m 3 . 
     
     
         9 . The process as claimed in  claim 1 , wherein the mixer comprises a stirring rotor. 
     
     
         10 . A process for preparing an aromatic compound bearing at least one aldehyde group —CHO para to a hydroxyl group, comprising:
 preparing an aromatic compound bearing at least one —CHOH—COOH group para to a hydroxyl group, according to the process of  claim 1 , and 
 oxidizing the aromatic compound bearing at least one —CHOH—COOH group para to a hydroxyl group. 
 
     
     
         11 . The process of  claim 2 , wherein the at least one aromatic compound is selected from the group consisting of guaiacol, guetol, and mixtures thereof. 
     
     
         12 . The process of  claim 6 , wherein the condensation reaction is performed in a cascade of at least two reactors. 
     
     
         13 . The process of  claim 6 , wherein the condensation reaction is performed in a cascade of at least three reactors. 
     
     
         14 . The process as claimed in  claim 8 , wherein the specific mixing power of the mixer is between 0.1 kW/m 3  and 10 kW/m 3 . 
     
     
         15 . The process as claimed in  claim 8 , wherein the specific mixing power of the mixer is between 0.1 kW/m 3  and 5 kW/m 3 . 
     
     
         16 . The process as claimed in  claim 9 , wherein the stirring rotor is selected from the group consisting of radial rotors, axial rotors, combination rotors, mechanical blending rotors, and rotors suitable for viscous media or media containing solids.